Machine and appliance for cutting or forming screw-threads.



G. H. ALEXANDER. MACHTNE AND APPLIANCE FOR CUTTING 0R FORMING SCREWTHREADS.

APPLICANQN min MAY 2, 1914. 1,173.97. Paiented Ee'b. 22,1916.

l2 SHEETS-SHEET 1.

EllllllllllIllllllllllllllll Mlllllillllllllllmlllll Mllllllim FigiWITNESSES INVENTOR G. H. ALEXANDER. MAcHlNE AND APPUANCE Foe CUTTING 0Rmamme SCREW THREADS.v

Patented Feb. 22, 1916.

2 SHEETS-SHEET 2.

APPLICATION FILED MAY 2.

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WHNESSES Figi) Figi4.

SYM

ATTORNEYS' v- Meerane AND emmene-n' non CUTTING onronmine scnnWV-rnnnenstmarne.

TocZZ whom/t may concern y.15e it known that I, GEORGE HENRYALEX-Antolin, subject of the King of Great Brit- .a-in, residing at Doestreet, in the cit-y of' Birrainglmni, England., engineer, `rave1nyented certain new and useful improvements Relating' to lrl'achiims`and Appliances for Cutting or Forming crewlgTlnfeads, of which thetollowingsis a s neication. This invention hasfor its object to provide:for the more ready and effective cut ting or forming of screw threadsupon rods f and other parts of iron, steel or other metal.

It has previously been proposed to employ a'screwthreaded mill or cutterof the saine pitch as the .ee-row to he produced and scV'-- eral timeslnirg'er in diameter. the mill he ing rotated at the saine rate as thepiece and advanced on to the saine in [al direction at right angles tothe axis ofthe 'Work piece. r/lrccordiitg to my experience this device.possesses the disadvantage that smalli'acets are produced thereby on thethread ot the work piece. l

The present invention, hy which the Said disadvantage is avoided.comprises the use of a screwA threaded mill like rotating tool havingmultiple start thread of the saine pitch as that required on the Workpiece and rotating relatively to the Work pieceat a rate which inverselyproportional to the niirnher of starts ony the mill. By pitch is meantvthe distance bctwen any one ridge and the next.

In the tivo accompanying sheets :of explanatory drawings z-F igure l isaside elevation and Fig'. 2 a` front Aelevation illustrating;diagrannnatically. a machine adapted for cutting screw threads inaccfrndafnce with this invention. Figs. and 4 are views showing' thetool and Work in Contact 1with 'each other, the views illustrating theinanner of cutting the single start thread on the Work hy atwo-startthread on the tool.

Upon the chuck or work' holder a of a screwing machine or lathe issecured a spiral Wheel Z) which rotates a similar spiral wheel c securedonthe spindle (l. On the latter is mounted a spiral Wheel e gearing witha spiral Wheel f on a slide g. The wheel c can slide along the spindle(Z. Rotation of the said wheel by the spindle is effected by a featherkey, spline, or its equivalent. The

spindle L ot the iyh'eel f carries a p inion z' gearing with a pinion jon the spindle 7c' which' is situated parallel with the axis of GeenenHENRY .arnxennnn or nnmnonam, .Eno-'Illini Specification of ILettersPatent.

Application ld May 2, 1914. Serial No. 835,914.

Work

i 1 baction, the cross slide or its-'equivale Patentamt esta the workholder a. oaithe'spiaai il. cent the chuck or Worltlliolder;ther f themill like toolllfc if adapted'for the desiredl t piece as m which issecuifedjii l i by the chuck. The tool Zlisipr'oi l a 'screw threadfoi-med aroundtl i hery of the tool and also longitudn l rother`groot-'es for clearance and'cuttuig 1kposes. 65

The pitch of the `vthreadis 'identical with. that to be cut, andtheshapeof the thread is made as nearly like thatto he' 'clit sifpossible. Ordinarily the' threadworif thefftool is a. little narrowerthathe grooiejtd he cut'in theworlr pieceyfthe amount ofthe differencedepending onf the d 'iarneterIogjthed tool. Usually the toolisfeonside'rably larger in diameter than the forli pilecdffour tofivetimes being found conienientin practice.

To bring' theaforesalid ssreiifilnrftoo nto advanced, e. g. by acaiiifafctlfla-tfedllefr n or other device. Such.niovernPfbfinsLthe toolup to and into flageni-entfiv A @the Work piece. The advance of thfenrosjslide is continued until thelrequired thr dfkhas been cut or formedl011 the Work 'piece'.s

Instead of employinga single start thread on the tool Z as heretoforethe tool is At'ornned withl a two-start or other multiple thread and thespeed of the tool is proportionately less. That is to say, with a.twoistart tool cutting a single start thread `on the Work piece,'therate of rotation of the tool is one 90 half that of the work piece. Bythe use of a multi-start thread on the tool a smooth thread Withoi'ltfacets is produced on the Work piece and an advantage 'is gained inoperation inasmuch as the peripheral speed of the tool is considerablyless than when the tool is formed with a single start thread and rotatedat the saine speed as the Work.

The manner in which a Single thread iS. out on the work by a two-startor other multiple thread on the tool is illustrated in Figs. 3 and 4.

Fig.- 3 shows the outline of a 'screw in Contact with the periphery ofthe milling tool. From this it is evident that so long. as thedimensions of the grooved portions of the/tool are the same as thethre'adthe two parts must roll together no matter whether the tool has asingle or a multistart thread formed o n it. v' The condition is not thesameras when a screw engages a nut. Thisu perhaps ismade clearer byFig.

- one half of a thread on the upper side of the job and the direction ofthe corresponding thread on the tool which, of course, lies on theunderside of the tool. It is understoodv that the two pieces rotate inthe same direction. that is to say the contacting parts are moved inopposite directions.

Starting at a. Fig. 4, where the job and tool touch, the point of thethread on the tool will cut into the job. Proceeding slowly through onehalf a revolution, when the point b on the job reaches the tool, the corresponding point Z) on the tool will coincide with that point.I if thetool is formed with a single-start thread and is rotated at the Samenumber of revolutions as the job. Between the points a and b every pointon the 'tool will meet a corresponding point on the job and consequentlyduring half a revolution, half the thread will be cut by the tool.Assuming the tool -to be formed with a two-start thread. then theextreme end of the half thread on the tool will be at thepoint c Fig'.4, andas this is twice the distance correspondingto,points a and b onthe job it follows that in `order that a line corresponding to c6, Z),shall be cut on the job the tool must be rotated at half the speed.Thevpoint c on the tool will then coincide with the point b consequentlyduring a quarter of a revolution of the tool half a thread will be cuton the job. The number of starts on the tool makes absothread cut on thejob so long as the rela-tive speeds of the tool and job are in theproper proportion. As before stated the threads on the toolhave to bemade rather narrower than the grooves to be cut on the job because thelines of the two threads cross'wher the job and tool touch, but thepitch of the threads is the same.

Ordinary parting or cutting off vand iinishing tools 1na7 be employedwith the'cross slide carrying the screwing tool aforesaid.

The invention is applicable to lathes or screwing machines 'of varyingtypes as employed to meet varying services .or requirements.

Having thus described mv invention what I claim as new and desire Vtosecure by Letters Patent is :-v

In screw cutting appliances of the tvpe in which is employed a screwthreaded mill like rotating tool adapted to cut or form.

the required screw threads around the rotating work piece when advancedon to the same by a movement atright angles to the axes of the tool andwork piece, a tool having a multiple start thread of the Same pitch asthat to he cut and rotating relatively to the work piece at a speedwhich is inversely proportional to the number of `Starts on the mill.

In testimony whereof I have signed my name to this specification in thepresence 'of two subscribing witnesses.

GEORGE HENRY ALEXANDER.

Witnesses:

JOHN MORGAN, FRANCIS MALPr-is.

